<!doctype html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport"
        content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>js循环结构之do..while</title>
</head>
<body>
  <script>
    function star(row = 5) {
      let start = 0
      do {
        let num = 0
        do {
          document.write('*')
        } while (++num <= start)
        document.write('<br/>')
      } while (++start <= row)
    }
    star()
    star(20)
  </script>
</body>
</html>